I. Technical Field
The present invention relates to a robot arm in which the influence of collisions against personnel or obstacles can be mitigated.
II. Description of the Related Art
Various conventional technologies have been proposed for cushioning impact forces derived from collision with an obstacle or from collision avoidance.
For instance, Japanese Patent Application Laid-open No. 2005-59171 discloses a technology wherein, after detection of a collision between a robot arm and an obstacle, the direction of current flowing in a motor that drives a joint that couples an arm with an arm is reversed, to apply thereby, to the arm, torque that is the reverse of torque before the collision.
When reverse torque is applied to a conventional robot arm, through inversion of the current flowing through a motor, the robot arm slows down, stops and then reverses. This gives rise to a commensurate delay in the motion whereby the robot arm moves in a collision avoidance direction or in a withdrawing direction in which the impact force of the collision is mitigated. Ordinarily, the motor output of conventional robots has a built-in reducer for generating driving torque. Accordingly, the motor runs at comparatively high revolutions during operation of the robot arm, and hence the time elapsed from motor slowdown to reverse is apt to be substantial. That is, conventional robot arms are problematic in that the time elapsed until robot arm reversal is long, and in that the responsiveness of the reversing action for collision avoidance and/or for impact force cushioning is insufficient.